Refineries typically obtain crude oil from a number of sources having different characteristics such as viscosity, density, sulfur content, salt and other impurities, etc. Each of these crudes are delivered to a refinery via pipelines, ships and other crude carriers and stored in large tanks until the refinery is ready to refine it. Typically, a refinery works to blend various crudes in preferred proportions recognizing that each of the various crudes have different levels of their constituent components, both good and bad, in an attempt to optimize the utility of the various systems with that specific refinery. One of the first operations in the refinery for processing the crude oil is to remove salt and other contaminants from the crude. Salts that are typically found in crude oil are chlorides of sodium, magnesium and calcium and it is necessary to remove these salts to avoid the creation of hydrochloric acid within the refinery which is highly corrosive. Salt is typically removed by injecting clean water into the crude oil such that water droplets are dispersed into the crude oil such that any salt in the crude may be captured or transferred into the water. To absorb the greatest amount of salt, it is generally desired to create a great number of reasonably small water droplets in the crude oil to transfer the salt into those droplets. However, the refinery operator wants as little water taken up into the refinery from the desalter system as possible. So while it is desirable to have a lot of very small droplets, it is also desirable that a minimal amount of water is put into the crude oil and that the water droplets are amenable to being quickly and easily removed from the crude oil after the salt has been captured by the water droplets.
As the water must be removed, the droplets are typically removed based on density differences between the crude oil and the water by allowing the emulsion to rest in a large settling vessel where the heavier water settles to the bottom. Unfortunately, this can be a slow process, especially when the droplets are very small and tend to settle very slowly. This problem is particularly challenging for more viscous and denser crude oils. One approach to aid removal of the water droplets is to reduce the viscosity of the crude by heating. So, it is not uncommon for refineries to heat the crude oil as it comes into the desalter system to reduce the effective viscosity of the crude oil and accelerate the rate that droplets descend to the bottom of the settling tank.
Another approach has been to increase the coalescence of water droplets by imposing an electric field that cause the water droplets to be concentrated together and form larger droplets that separate faster. Other coalescer technologies where the emulsion is gently mixed to again bring the water droplets together to coalesce have been proposed.
Clearly, refineries work best when the crudes have less undesirable materials dissolved therein and any opportunity to efficiently and simply remove such contaminants from the crude oil would be well received by refinery operators.